Sintered carbides



United States Patent 3,322,513 SINTERED CARBIDES Robert B. Corbett, Mars, Pa., assignor to Metaltronics, Inc., Pittsburgh, Pa. N0 Drawing. Filed Oct. 4, 1965, Ser. No. 493,307 8 Claims. (Cl. 29182.7)

This invention relates to a new class of precipitation hardenable sintered carbides. More specifically this invention relates to an improved sintered carbide class of compositions having cobalt or nickel base binders which are hardenable by precipitation hardening means. In the application of the principles of this invention, parts such as draw dies, gages, lamination dies, heading dies and the like, are made from carbides of refractory metals in a hinder or matrix which consists of alloys of cobalt and/ or nickel containing precipitation hardening elements. On precipitation heat treatment the die dimensions can be controlled and made to compensate for wear and to provide for reuse of the tool and longer tool life.

Sintered carbides as made by the methods of the prior art are powder metallurgy products and consist in finely divided, hard particles of carbides of refractory metals in .a binder or matrix to form a product characterized by high hardness, wear resistance, temperature resistance, and high compressive strength.

The hard particles are generally tungsten carbide in combination with lesser amounts of carbides of other refractory metals including titanium, tantalum, columbium, molybdenum, vanadium, chromium, or Zirconium. In fact any of the carbide forming elements may be used as a carbide in the sintered refractory Cemented carbides. The binder is generally cobalt or nickel.

The carbides exist as individual grains and the binder, which is usually cobalt, is present in the interstices as substantially pure metal. While either cobalt or nickel may be used as the binder, cobalt is generally preferred as the solubility of tungsten carbide is less in cobalt than in nickel. Also cobalt has somewhat better adhesive properties with relation to tungsten carbide at elevated temperatures.

Cemented carbides while excellent for Wear resistance, suffer the disadvantage that they are very expensive to purchase and to shape, and there are no economical and satisfactory methods available to increase their dimensions to compensate for wear. High temperature cobalt and nickel base alloys are precipitation hardening and can be made to increase their volume on precipitation hardening. Therefore the present invention contemplates the development of cemented carbides having a matrix consisting of a cobalt or nickel base alloy which approximates the standard cobalt and nickel base high temperature alloys in composition, and which is expandable in volume on precipitation heat treating.

Improved carbide compositions with the wear resistance, red hardness, and high compressive strength of the conventional carbides and capable of being precipitation hardening to increase their volume to compensate for wear and to permit reuse and longer life, will fulfill a long felt need in industry.

In view of the foregoing an object of this invention is to provide a new family or class of cemented carbides which are hardenable by precipitation hardening means to increase their volume to compensate for wear.

Other objects and advantages will be apparent from the description which follows.

There are definite limitations to the age hardening or precipitation hardening process which is basically quite different from hardening by quenching. Fundamentally,

precipitation hardening involves three steps as follows: (1) The development of a concentrated solid state solution at a relatively high temperature. (2) The retention of that solution at lower temperatures where it would not normally exist since relative supersaturation would result. (3) The controlled precipitation of the solute within the matrix.

In order for this to be accomplished the base metal must be capable of holding the precipitating elements in solid solution. Any alloy system which shows a decreasing solubility with temperature may be precipitation hardenable. The first treatment is termed solution treating and it is only after the second or reheating treatment that precipitation hardening occurs. For a further discussion of the principles of precipitation hardening reference may be made to a book Elements of Physical Metallurgy by A. G. Guy, copyright 1959, published by the Addison Wesley Publishing Co., Inc.

The precipitation hardening process normally results in an expansion which may be as much as 0.0045 inch per inch for 17-4 PH precipitation hardening stainles steel when solution treated from about 1750 F. followed by aging at about 850 F. to about 1050 F. Most of the cobalt and nickel base alloys do not exhibit this degree of change although they do expand in volume on precipitation' hardening. Generally the change encountered on precipitation hardening the cobalt or nickel base alloys is less than about two thousandths of an inch per inch.

My investigations show that with a carbon content of the binder of about 0.05 to 0.35% and with the use of relatively high solution hardening treatments, as Will be more fully explained hereinafter, a linear expansion of at least about 0.0003 inch per inch is obtainable on precipitation hardening the improved carbide compositions of this invention.

The compositions of some of the cobalt and nickel base high-temperature alloys are included in a chapter, Wrought Heat Resisting Alloys, in a book, Metals Handbook, vol. 1, 8th Edition, copyright 1961, published by the American Society for Metals, Novelty, Ohio, pp. 466-488. The compositions listed do not represent a complete list and are cited as typical of many standard commercial compositions of cobalt and nickel base, high temperature alloys.

The cobalt and nickel base high temperature alloys are classified as austenitic alloys and they exhibit superiority at temperatures above about 1100 F. These alloys are hardened by precipitation hardening means through the addition of such elements as tungsten, columbium, titanium, molybdenum, chromium, aluminum, boron, nitrogen, beryllium, and zirconium all of which have limited solubility in the cobalt or nickel base metals.

Listed herewith in Table 1 are nine standard grades of cemented carbide which represents grades in commercial use.

TABLE 1 Carbide Carbide Cobalt, Hardness Density, Group percent Rockwell A g./cu. cm.

TaC 'liO WC In developing the precipitation hardening, sintered carbides in accordance with the principles of this invention, the nickel or cobalt binder is replaced with a nickel or cobalt precipitation hardenable composition. I find that it is necessary for an appreciable precipitation hardening effect that the combined cobalt plus nickel content of the precipitation hardenable carbide be at least about 6%. Also the carbon content of the binder should be between about 0.05 to about 0.35%.

The method of replacing the cobalt or nickel binder with a precipitation hardenable composition in accordance with the principles of this invention will be apparent from the following examples. Included in the examples cited is the normal composition of the standard carbide and the matrix composition which in the examples shown is cobalt. Also included is the composition of the improved precipitation hardening carbide in accordance with the principles of this invention. It will be noted that the cobalt binder of the standard carbide has been replaced With a precipitation hardening, nickel or cobalt base alloy. All percentages are by weight.

Example 1 Nominal composition of sintered carbide B:

Percent Tungsten carbide 88 Tantalum plus Titanium carbide 1 Cobalt l1 Nominal composition of S 816 cobalt base alloy:

Percent Carbon .40 Chromium Nickel 20 Cobalt 43 Molybdenum 4 Tungsten 4 Columbium 4 Iron 4 Composition of precipitation hardening sintered carbide: Percent Tungsten carbide 88 Tantalum plus Titanium carbide 1 Binder 11% (ODS-0.35% carbon) Chromium 20 .11 2.20 Nickel 20 .11 2.20 Cobalt 43 .11 4.73 Molybdenum 4 .11 .44 Tungsten 4 .11 .44 Columbium 4 .11 .44 Iron 4 .ll .44

The balance is minor elements such as manganese, silicon, sulphur etc.

Composition of precipitation hardening sintered carbide: Percent Tungsten carbide 88 Tantalum plus Titanium carbide 1 Binder 11% (ODS-0.35% carbon) Chromium 19 .11 2.09 Nickel 57.5 .11 6.33 Cobalt 14 .11 1.54 Molybdenum 4 .11 .44 Titanium 3 .11 .33 Aluminum 1.3 .11 .14 Iron 1 .11 .11

The balance is minor elements such as manganese, silicon, sulphur etc.

Example 3 Nominal composition of sintered carbide C:

Percent Tungsten carbide 75 Tantalum plus Titanium carbide 2% Cobalt 22 /2 Nominal composition of L 605 cobalt base alloy:

Percent Carbon .15 Chromium 20 Nickel 10 Cobalt 51 Tungsten 15 Iron 2 Composition of precipitation hardening sintered carbide: Percent Tungsten carbide 75 Tantalum plus Titanium carbide 2.5 Binder 22 /2% (0.05-0.35% carbon) Chromium 20 .225 4.5 Nickel 10 .225 2.25 Cobalt 51 X .225 11.48 Tungsten 15 .225 3.38 Iron 2 .225 .45

The balance is minor elements such as manganese, silicon, sulphur etc.

Example 4 Nominal composition of sintered carbide F:

Percent Tungsten carbide 77 /2 Tantalum plus Titanium carbide 11 /2 Cobalt 11 Nominal composition of V 36 cobalt base alloy:

- Percent Carbon .25 Chromium 25 Nickel 20 Cobalt 43 Molybdenum 4 Tungsten 2 Columbium 2 Iron 3 Composition of precipitation hardening sintered carbide: Percent Tungsten carbide 77.5 Tantalum plus Titanium carbide 11.5 Binder 11% (ODS-0.35% carbon) Chromium 25 .1l 2.75 Nickel 20 .11 2.20 Cobalt 43 .11 4.73 Molybdenum 4 .11 .44 Tungsten 2 .11 .22 Columbium 2 .11 .22 Iron 3 .l1 .33

The balance is minor' elements such as manganese, silicon, sulphur etc.

Composition of precipitation hardening, sintered carbide:

Percent Tungsten carbide 65.5 Tantalum plus Titanium carbide 24 Binder 10 /2% (0.05-0.35% carbon) Chromium 19 .l05 2.00 Nickel 52.5 .105 5.51 Cobalt 11 .105 1.16 Molybdenum 10 105 1.05 Titanium 3 .l05 .32 Aluminum 1.5 .105 .16 Iron 3 .l05 .32

The balance is minor elements such as manganese, silicon, sulphur etc.

It will be noted that the combined nickel plus cobalt content of the precipitation hardenable sintered carbides illustrated in Examples 1 through 5 are 6.93%, 7.87%, 13.73%, 6.93%, and 6.67% respectively. These are all over about 6% combined cobalt plus nickel which I find necessary to achieve a pronounced volume change in the sintered carbide on preciptiation hardening. 10% or over cobalt plus nickel is preferred as in the Example No. 3 where this value is 13.73%. On the other hand the cobalt plus nickel content should not be over about 20% as the hardness of the sintered carbide will be too low for most wear applications.

Also I find that the total percent of refractory carbides should be between about 60 to 94% by weight.

In addition the binder or matrix should contain one or more precipitation hardening elements such as tungsten, columbium, titanium, molybdenum, chromium, aluminum, boron, nitrogen, beryllium or zirconium in sufficient quantity to obtain a pronounced precipitation hardening effect.

I find a relatively large increase in volume and increased dimensional change occurs when the carbon content of the binder is about 0.05 to about 0.35% in combination with a relatively high solution hardening temperature. While precipitation hardening is predominant it is quite likely that other hardening mechanisms such as multiphase hardening and martensitic hardening are also involved to a minor extent. With the carbon over about 0.35%, martensitic hardening occurs to a greater extent.

While the matrix or hinder compositions may resemble compositions used for high temperature applications, the objectives and results are altogether different. The primary objective in high temperature alloys is to provide heat resistance and creep resistance primarily for aircraft and missile applications. As a precipitation hardening binder for cemented carbides in this invention, the

primary objective is to provide for expansion on heat treating. For this purpose I find a solution hardening temperature of about 1750 F. to about 2300 F. followed by oil quenching and aging at about 1000 F. to about 1600 F. for several hours to be satisfactory for the alloys listed in the Examples 1 through 5. Cold treating at l20 F. to --l50 F. is also beneficial in obtaining a further increase in volume. For a draw dies and dies with cavities it is sometimes desirable to complete the precipitation hardenng treatment under constraint to obtain greater closure at the hole. Also this invention includes the modification wherein the precipitation hardenable carbide is partly aged to obtain a partial increase in volume to compensate for wear or undersize and later the precipitation hardening cycle may be completed to obtain another increment of increased dimensional change. Also the precipitation hardening cycle can be repeated many times and an increase in volume will occur after each treatment to provide for compensation for wear or undersize condition.

Having described my invention in terms of several examples, it will be understood that the invention may be otherwise embodied within the scope of the following claims.

I claim:

1. A precipitation hardenable sintered carbide, consisting essentially of about 60 to about 94% of refractory carbides in a binder of a cobalt group metal selected from the group consisting of cobalt and nickel, said binder containing about 0.05 to about 0.35% carbon and several precipitation hardening elements from the group of refractory metals consisting of tungsten, columbium, titanium, molybdenum, chromium, and vanadium; said carbide containing about 6 to 40% of combined cobalt plus nickel.

2. A precipitation hardenable sintered carbide consisting essentially of about 60 to about 94% of refractory carbides in a binder of a cobalt group metal selected from the group consisting of cobalt and nickel, said binder containing about 0.05 to about 0.35% carbon and several precipitation hardening elements from the group consisting of aluminum, beryllium, boron, and nitrogen; said carbide containing about 6 to 40% of combined cobalt plus nickel.

3. An improved cemented carbide composition consisting of refractory carbides in a precipitation hardenable binder, said carbide composition inclu-dng about 60 to 94% refractory carbides and about 6 to 40% combined nickel plus cobalt, said precipitation hardenable binder containing about 0.05 to about 0.35 carbon and several precipitation hardening elements, said carbide composition being characterized by a linear expansion of at least 0.0003 inch per inch on precipitation hardening.

4. A precipitation hardenable cemented carbide composition consisting of refractory carbides and a binder; said refractory carbides comprising about 60 to 94% of the total carbide composition by weight, and the said binder being a cobalt group metal selected from the group consisting of cobalt and nickel, said carbide composition containing about 6 to 40% combined cobalt plus nickel, and the said binder containing about 0.05 to about 0.35 carbon by weight in addition to one or more precipitation hardening elements, the said cemented carbide composition being characterized by an increase in volume on precipitation hardening.

5. A precpitation hardenable, cemented carbide composition containing about 60 to about 94% of refractory carbides, and the remainder being a cobalt base, precipitation hardening alloy with about 0.05 to about 0.35 carbon.

6. A precipitation hardenable cemented carbide composition containing about 60 to about 94% of refractory carbides, and the remainder being a nickel base, precipitation hardening alloy with about 0.05 to about 0.35% carbon.

7. A precipitation hardenable sintered carbide containing about 60 to 94% by weight of refractory carbides, the balance of the alloy being formed of a precipitation hardenable matrix of a cobalt group metal selected from the group consisting of cobalt and nickel; the said precipitation hardenable matrix containing about 0.05 to about 0.35% carbon and one or more precipitation hardening, tungsten group elements selected from the group consisting of tungsten, columbium, titanium, molybdenum, chromium, and vanadium.

8. A precipitation hardenable sintered carbide composition containing about 60 to 94% by weight of refractory carbides, and the balance being a precipitation hardenable matrix in which the carbon content is about 0.05 to about 0.3 5% carbon.

References Cited UNITED STATES PATENTS 1,815,613 7/1931 Comstock 29-l82.8 5 2,121,448 6/1938 RitZau 29l82.8 2,986,807 6/1961 Elbaum 29-1828 3,053,706 9/1962 Gregory 29-182.8

FOREIGN PATENTS 378,055 8/1932 Great Britain.

CARL D. QUARFORTH, Primary Examiner.

BENJAMIN R. PADGETT, Examiner.

15 A. J. STEINER, Assistant Examiner. 

1. A PRECIPITATION HARDENABLE SINTERED CARBIDE, CONSISTING ESSENTIALLY OF ABOUT 60 TO ABOUT 94% OF REFRACTORY CARBIDES IN A BINDER OF A COBALT GROUP METAL SELECTED FROM THE GROUP CONSISTING OF COBALT AND NICKEL, SAID BINDER CONTAINING ABOUT 0.05 TO ABOUT 0.35% CARBON AND SEVERAL PRECIPITATION HARDENING ELEMENTS FROM THE GROUP OF REFRACTORY METALS CONSISTING OF TUNGSTEN, COLUMBIUM, TITANIUM, MOLYBDENUM, CHROMIUM, AND VANADIUM; SAID CARBIDE CONTAINING ABOUT 6 TO 40% OF COMBINED COBALT PLUS NICKEL. 